The ingestion of breast milk plays an important role in the acquisition of early immune functions by newborns. In particular, colostrum secreted just after delivery contains IgA antibodies and many substances involved in immune functions and plays an important role in the defense of newborns against infection. The substances involved in the immune function include proteins called chemokines and CXCL8 (IL-8), CCL5 (RANTES), and CCL28 are known as chemokines comprised in the breast milk. However, for example, it has been reported that almost no expression of CCL28 is found in the mammary tissue at the time of colostral production and secretion. Thus, it is still unknown how chemokines are involved in the acquisition of immunity by the newborns through the colostral ingestion.
Other than the above chemokines, chemokines discovered in the murine and human thymus and involved in intestinal immunity include Chemokine (C-C motif) ligand 25 (CCL25). The possibility that CCL25 is involved in the transition of IgA to the colostrum in the mammary tissue as a function of CCL25 in the mother's body has so far been reported (Non Patent Literature 1). However, it has not been clear yet how CCL25 serves in the acquisition of immunity by newborns through the colostral ingestion.